1. Field of the Invention
The present invention relates to a linear actuator in which an internal movable member reciprocates along a hole of a tube member under the driving action of a rotary driving source. An external movable member including a slider provided outside of the tube member can be displaced integrally with the internal movable member.
2. Description of the Related Art
A magnet type rodless cylinder has been conventionally used as a mechanism for transporting or positioning a workpiece or the like. The magnet type rodless cylinder includes a piston which reciprocates along a hole of a cylinder tube under the action of a pressure fluid supplied into the cylinder tube, and a slider which surrounds the outer circumferential surface of the cylinder tube. The reciprocating motion of the piston is transmitted to the slider by the magnetic force of magnets which are incorporated into the piston and the slider respectively to integrally displace the piston and the slider.
The present applicant has suggested a rodless cylinder comprising a support rib for a cylinder tube which can keep the cylinder tube and a slider being out of contact with each other even if the displacement range of the slider is increased. The above rodless cylinder reduces generation of the dust and can be preferably used in an environment where the cleanness is required. The environment includes clean rooms for the medical purpose, the food manufacture, the semiconductor production steps or the like (see U.S. Pat. No. 6,148,714).
It is a general object of the present invention to provide a linear actuator which makes it possible to highly accurately stop, at an arbitrary intermediate position, an external movable member which is displaceable integrally with an internal movable member in an environment where the cleanness is required.
It is a principal object of the present invention to provide a linear actuator which makes it possible to smoothly displace the external movable member upon the start or the stop thereof.